Excellent Metal Phosphide Electrode for Potassium Ion Hybrid Capacitors: The Case of Carbon Nanotube-Wrapped AgP2

Abstract

Potassium-ion hybrid capacitors (PIHCs) have received extensive attention due to combining the advantages of high energy density of batteries and high power density of capacitors and are economically advantageous alternatives to lithium-ion hybrid capacitors. Metal phosphides are potential anode materials for K+-storage with high theoretical capacity, relatively low working potential, thermal stability, and metal characteristics. Nevertheless, high-performance metal phosphide materials for PIHC applications have proven to be challenging due in part to the dissatisfied electronic conductivity, irreversible deterioration of the structure, and high electron transfer resistance. In this work, we synthesize carbon nanotube (CNT)-wrapped AgP2 via a wet-ball milling (WBM) approach to prepare the electrode slurry. Simultaneously with electrode cycling, the in situ formed Ag nanocrystals increased the electrical conductivity and formed Ag-P composites that easily adsorbed more K+, the framework of CNTs effectively reduced the capacity fading caused by material refinement, and a large surface area is provided to facilitate electrolyte penetration. Owing to these advantageous merits of AgP2/CNT electrodes, the assembled PIHC exhibits a high energy/power density of 37.3 Wh kg–1/12207.3 W kg–1, respectively, and remarkable cycling life over 2000 cycles. These promising results reveal that the design interfacial engineering of the CNT-wrapped AgP2 scaffold provides a clue to propel the development of metal phosphide-based hybrid capacitors.